Plywood panel



- u 9, 1942- V D. II4DESKEY 2,286,068.

PLYwoon PANEL Filed May 25, 1940 3nventor v an Donald Deskey v attorneysPatented June 9, 1942 PLYWOOD PANEL Donald Deskey, New York, N. 1.,assignmto United States Plywood Corporation, New York, N. Y.. acorporation of New York Application May 25, 1040, Serial N0. 337,219

7 Claims. (Ci. -89) Plywood panels, especially of soft woods. such asDouglas fir, are generally made of rotarycut veneer, dried, laid up withthe grain in the core at right angles to the grain in the faces, andglued together, The largest part of domestic production is of Douglasfir, and of this, three-ply wall board panels 4 feet wide by 8 feetlong, constitutes a large percentage.

One of the objections to the use of such panels, in walls, arises fromtheir tendency to separate at their abutting edges, and in theoccasional checks and cracks which appear in the surface of the panels.Wood shrinks, in drying, and the panels, though made of dried veneer,nevertheless normally lose moisture after their installation, In thedrying out process panels which have been placed in edge-abuttingrelationship, with their grain generally parallel, will shrink in time,and an open Joint is left. This shrinkage is thus manifestedparticularly transversely of the grain. Shrinkage creates stresses inthe various plies. Over their entire area the face plies are subject tostresses directed parallel to the panel's plane and transversely oftheir grain, resulting in checking or even in cracking, but at theiredges in particular do such transverse stresses accumulate to produce anexcess of shrinking (or swelling), and resulting edge separation.

Douglas fir, moreover (and like coniferous wood, e. g., pine of varioussorts), has very decided graining, particularly when made fromrotary-cut veneer, as is practically all commercial veneer. The fibersin the soft spring wood are less closely packed than in the contrastingharder summer and fall growth. The denser summer and fall wood, whensubjected to moisture, swells more greatly than the spring wood, andaccentuates the grain, making it visible even under paint or otherfinish coating.

It is often desirable to bend plywood around curves, particularly inexecuting modern architectural designs, but the stresses thus producedin the convex face ply. and the added present or future tendency tochecking, cracking, swelling, and even laminar grain separation, deteror limit such uses, even more than the actual resistance to bendingof-the core.

I have found it possible to eliminate these stresses, and thedeleterious effects thereof, by gouging the surface or surfaces of thepanel with a multitude of closely spaced grooves, extending generallyparallel to the grain, and preferably of uneven, irregular, and randomdepth, following no recurring pattern, but sufliciently closely spaced,and having, at sufficiently close intervals, sumcient depth as to cutthrough the recurring grain layers, and to break up each individuallayer and the surface of the panel generally into narrow widths or ribsof uncut wood. Within these narrow widths the which cause the shrinking,cracking, checking, and swelling may not accumulate to such an extentthat they may not be relieved within the grooves in the surface.

Accompanying this application is a sample of a piece of plywood, thusgrooved, and photographs showing such a panel before grooving and aftergrooving.

The accompanying drawing attempts to illustrate the appearance of thepanels, and the manner in which the objectives are attained.

Figure 1 is an end view of two panels, viewed as in a section through awall, showing the panels grooved on one surface only.

Figure 2 is a section through a wall, showing panels grooved on bothsurfaces, and differently supported.

In the drawing the panels I and 2 are shown with grooves l in onesurface only-that surface which is exposed when installed-whereas thepanel 3 is shown with grooves 4 and I in its oppomte surfaces. Thisgrooving is preferably in the face ply I or 6' only, and does not extendpast the glue line I or I. The panels land 2 are secured (as by nailing)in edge-abutting relationship (indicated at I) to a support such as thestud s. The panel I is secured upon a wall surface It by a mastic IIthat enters the grooves 5.

The grooving may be done after sanding the panel's surface, butpreferably this step is omitted, for the grooving in itself removestapes and obscures patches, and completely alters the surface. Thegrooving may thus take the place of the sanding, and no extra handlingis necessary. The grooves may be formed in various ways, preferably byplanar knives having irregularly serrated cutting edges, but it might bedone by a plurality of thin disc-like knives r saws, closely spacedalong an arbor. The grooves need not conform, in cross-section, to anyparticular form, but may be V-shaped, roimded, or individually ofdifferent contours. Whatever the instrumentallty used, each individualgroove should be reasonably continuous and of the same depth, from endto end, through soft spring growth and hard summer and fall growth, forany material discontinuity or variation in con,- tluuity, particularlyover an appreciable width or area,'will leave an area wherein stressesare cumulative. The grooving operation is performed by moving the panellengthwise (that is, in the direction of the grain) beneath the rotatinggrooving tool, or vice versa, to positively remove the wood from thegrooves and to leave upstanding ribs. Grooving of one surface only maybe sufficient in some instances. In other cases both surfaces aregrooved.

This grooving is to be distinguished particularly from grooving, asheretofore practiced, in patterns or groups of grooves, for purelyvisual effect. The grooving according to this invention is usuallydistinguished by an absence of any pattern. Moreover it is to beemphasized that while the visual effect is attractively rustic andinformal, and does enhance the salability of the product to those whodesire such effects, the grooving has as its principal objective theavoidance of undue shrinkage and swelling, and is of value for thatpurpose, and for the other purposes mentioned, regardless of appearance.

In the patterned grooving the grooves are so greatly spaced apart, andoccupy so small a part of the whole surface area, even at the edges,that they have no material effect in preventing the shrinking and edgeseparation of the panel, or in avoiding the harmful effects of shrinkingat or between the edges, whereas these are the principal functionaleffects arising from the type of grooving herein described, and theresults achieved by the herein disclosed grooving have not before beenattainable, neither by the patterned grooving nor by any other means ormethod known to me. If a patterned effect is desired, however, such maybe still within this invention, providing the grooves are closely enoughspaced, and sufliciently deep, to break up the continuity of the surfacelaterally, and to adequately groove the edge areas.

The essential of this invention is that the grooves are of such depth,relative to the thickness of the face ply, and are closely enoughspaced, that the ribs are of slight width, and the stresses in thegouged surface areas of the face ply are relieved, and can notaccumulate to any appreciable extent. Preferably the grooves do notextend to or through the glue line (glue meaning any adhesive such as isused or is suitable for use in plywood manufacture), but more or lessfrequently recurring grooves may extend almost to the glue line, withintervening grooves of lesser and irregular. depth. The grooves vary indepth, as the sample and photographs show, from mere surface scratchesto grooves of a depth to extend to or past the neutral plane of thegrooved face ply (halfway through the ply), some being of a depthapproaching the thickness of the ply itself.

The outer surface of the face ply being thus made discontinuous, thefibers in and Just beneath the original surface are separated from otherfibers at either side and the grain laminas are severed and ut through;stresses arising from shrinkage c n not possibly be transmitted norbuilt up cumulatively in lateral directions. The most they can build upis across the base of each rib, and each such stress is minute; if thereare sufficiently deep grooves, sufliciently closely spaced, thecumulative build-up of lateral stresses to an excessive value is veryeffectively prevented. Each stress is completely absorbed in its own riborslight width. The individual ribs swell or shrink accordingly, buthave. ample room for so doing, laterally within the grooves or outwardlyfrom the glue line, but always unnoticeably and harmlessly.

The irregular or wild graining of rotarycut veneer, of fir or likeconiferous wood which has pronouncedly different spring and autumngrowth, has already been mentioned. Many persons are pleased by thisgraining; others dislike it. The gouging process destroys the grainingpattern, by supplanting it with an obscuring pattern of parallel groovesof irregular or random depth, comparing one groove with another. Thismight be considered as objectionably monotonous, and hence noimprovement on the graining effect, but while the graining is no longerdiscernible as such, and while there is no part of the surface which isnot gouged, in many places where the grooving hits the summer wood thereis a very slight alteration in the direction or appearance of thegroove, and a break in the grain laminas, so that in the larger piece,there is not the monotony of perfectly straight and parallel lines. Thiseffect is obtained on rotary cut veneer, whereas it would not beobtainable in sawn lumberu The result is a visual impression of pleasingvariety, rather than monotony.

It is'in the relief of stresses and in the avoidance of checking,shrinking and edge separation that the gouged panels have their greatestfunctional advantage. Indeed, even should some small edge separationoccur between panels, the resulting crack would blend with the grooving,to such an extent that the crack would be virtually unnoticeable. Ifsome laminar separation of the grain does occur, it can only be verysmall in extent, as compared to smooth-surfaced panels, and lessnoticeable-indeed, quite iiivisible. Likewise, if checking or crackingdoes occur, as it might in isolated instances, the grooving willeffectively conceal it.

As has been noted, the grooving may be done only on that surface whichis to be visible after installation, and it will serve the intendedpurposes well. On the other hand, certain other or additional stressesmay be relieved if the two surfaces of the panel are thus grooved. Aplywood panel, the concealed surface of which is thus grooved, may beheld by cement upon a wall. The movement of the cemented surface inshrinking, if it is not grooved, breaks .the bond between the panel andits support. A similar panel, the cemented surface of which is grooved,does not break away from the supporting wall, because there is noaccumulation of stresses and shrinkage across the cemented surface. Thisoffers a means for attachment and support of such panels where nails andlike means can not well be used to support it.

Reference has been made to three-ply panels, to wall-board size panels,to panels the faces of which are rotary-cut, and to flr panels, butthese have been referred to chiefly because the invention will find itsgreatest field of usefulness with such panels, and yet the inventionmay, with corresponding advantage, be employed with panels of variousthicknesses, areas and sizes, of more than three plies, made, in part orwholly, of wood other than the woods specified, and in general, varyingfrom the panels described.

What I claim as my invention is:

1. As a new article of manufacture. a plywood panel having a face ply ofrotary-cut wood having pronouncedly different hard and soft growth, andconsequent wild g'raining when rotary-cut, the exposed surface of saidface ply having a plurality of substantially continuous grooves ofrandom depth over the surfaces, but each groove being of the same depththroughout its length, frequent grooves being of material depth to passthrough any hard growth layer encountered, said grooves extendingsubstantially lengthwise of the grain in said ply, and generally acrossits width, and being sumciently closely spaced to localize within theindividual ribs or groups of ribs the normal stresses arising fromshrinking, expanding and the like, and to prevent accumulation of suchstresses across any appreciable width. of the ply, and also to largelydestroy the normal srained eil'ect.

2. As a new article of manufacture, a plywood panel having amultiplicity of grooves in the exposed surface of at least one of theface plies thereof, frequent grooves being of substantial average depthrelatively to the thickness of said face ply, and each groove beingrelatively narrow and disposed closely adlacent other grooves, all ofsuch grooves extending substantially lengthwise of the grain of thewood, the depth of said frequent grooves and their frequency being suchas to prevent stresses, normally arising from shrinking and expanding,from accumulating across any appreciable width of the grooved ply.

3. As a new article of manufacture, a plywood panel having amultiplicity of grooves in the exposed surface of a face ply, saidgrooves being each sufllciently deep to prevent stresses, normallyarising from shrinking and expanding. from accumulating across anyappreciable width of the grooved ply, and of uniform depth throughoutits length, but of random depth relatively to other grooves, and eachgroove being relatively narrow, and disposed closely adjacent other suchgrooves, and all such grooves extending substantially lengthwise of thegrain of the wood.

4. A plywood panel as in claim 2, wherein the exposed surface of eachface ply is provided with grooves as specified.

5. As a new article of manufacture, a plywood panel having amultiplicity of grooves in the exposed surface of one face ply extendingsubstantially parallel to one edge of the panel and substantiallylengthwise of the grain of the wood, said grooves being each ofsubstantially uniform depth throughout its length, and of such depth asto prevent stresses, normally arising from shrinking and expanding, fromaccumulating across any appreciable width of the grooved ply, but ofrandom depth relative to other grooves, and being each of a width notappreciably exceeding its depth, and spaced without material intervalfrom adjoining grooves.

6. A grooved plywood panel as in claim 5, wherein certain deeper groovesare of a depth approaching or exceeding half the thickness of thegrooved face ply.

7. A plywood panel having, across the exposed surface of a face ply, amultiplicity of grooves, extending substantially lengthwise of the grainin such face ply, the grooves being each of substantially constantaverage depth throughout its length, but of random depth as compared toadjoining grooves, and being each narrow and deep, and closely adjacentother grooves, certain such grooves being so deeply cut that theirbottom is closer to the glue line than to the outer surface, and suchgrooves of all kinds being of sufficient frequency and narrowness, andsufficiently closely spaced, across the panel, to localize stressaccumulation within the width between grooves, and within the widthbetween such deeply cut grooves.

L DONALD DESKEY.

